Chapter 4 - Quadratic Functions and Equations - 4-2 Standard Form of a Quadratic Function - Practice and Problem-Solving Exercises - Page 208: 58

$a = -\frac{5}{2}$

First, we use distributive property: $3a + 12 + 2a - 2 = a$ Combine like terms: $5a + 10 = a$ Subtract $10$ from each side of the equation: $5a = a - 10$ Subtract $a$ from both sides of the equation: $4a = -10$ Divide both sides of the equation by $4$: $a = -\frac{10}{4}$ Simplify the fraction: $a = -\frac{5}{2}$